1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to a method of adjusting a photonic bandgap of a photonic crystal, a method of manufacturing a reflective color filter using the same, and a display device including the reflective color filter.
2. Description of the Related Art
Photonic crystals have a lattice structure in which at least two materials having different refractive indexes are periodically arranged in a two-dimensional or three-dimensional structure. The photonic crystals having the lattice structure have a predetermined wavelength band at which incident light cannot pass in any direction due to the periodical distribution of refractive indexes, which is called a photonic bandgap.
For example, when the photonic bandgap of a photonic crystal is formed on a region of a visible ray, and the frequency of light incident onto the photonic crystal corresponds to the photonic bandgap, 99% or more of the incident light is theoretically reflected from the photonic crystal. On the other hand, the incident light having a frequency outside the photonic bandgap is almost entirely transmitted through the photonic crystal.
The three-dimensional reflective properties are useful for manufacturing reflective color filters for display devices. In this case, reflective cooler filters having different photonic bandgaps according to R, G, and B pixels can be manufactured.
A method of manufacturing a three-dimensional photonic crystal is classified as a top-down method, in which conventional lithography is used, or a self-assembly method, in which the physical or chemical combination of a colloid particle or a polymer is used. Particularly, in the self-assembly method, a substrate (e.g., glass or the like) is perpendicularly arranged in a colloid solution having an appropriate size, and a crystal structure, in which colloid spheres are packed to one another, is formed using evaporation of a solvent and a capillary force. Thus, this method is advantageous in that the three-dimensional photonic crystal can be formed to have a large area and the crystal structure is good.
However, since it is difficult to control the fine colloid particles, many processes could be processed in order to control the photonic bandgap by patterning the crystal structure according to regions.
For example, each region of a photonic crystal having different photonic bandgap is manufactured using colloid particles with different sizes and refractive indexes. To form other colloids, templates are formed and removed. This operation affects the crystal structure that has been already formed, and increases the design limit and complicates the process when the crystal structure is formed with two or more colloid particles by repeatedly using the same process.
To overcome the above problems, Korean Paten Application No. 2003-0046142 discloses a method of forming a photonic crystal structure on a desired selective region of a substrate by controlling a colloid using an electric force.
FIG. 1 is a view for explaining a method of manufacturing a photonic crystal structure, which is disclosed in Korean Paten Application No. 2003-0046142. Referring to FIG. 1, a first electrode layer 22, a second electrode layer 25, and an insulating layer 28 are coated on a substrate 10. The first and second electrode layers 22 and 25 have respectively a first polarity and a second polarity in response to a direct voltage supplied from a direct power source 32. The substrate 10 is immersed longitudinally in a container containing a colloid solution 50, and then the substrate 10 is removed upwardly from the container at a constant velocity. Thus, due to a surface tension and a capillary force, the colloid photonic crystal is formed only on a region corresponding to any one of the first and second electrode layers 22 and 25 according to the polarity of the colloid particles of the substrate 10.
In the above method, a colloid structure is patterned by controlling the fine colloid particles using colloid self-assembly and rather than a template, an electric force is used. Thus, the method is advantageous in that a photonic crystal structure having various shapes and sizes can be manufactured according to the electrode design. However, the above processes must be repeated in order to form the photonic crystal structure having various bandgaps. For example, to manufacture a reflective color filter, a transparent electrode is patterned per pixel. In addition, to form R, G, and B subpixels, the entire substrate must be always immersed in different colloid solutions to grow the photonic crystal.